When this comes up there are a couple options.
1. If some of the heads just look sick I would suggest doing a hydrogen peroxide dip. There is a good thread if you do a quick search on what dose to use. I have done this successfully a number of times in the past but it only works if a head is sick and not already lost so much of the calyx that it is shedding over the leading edge.
2. With one of the first pictures I saw the shedding mentioned above. For this case I would first cut off the bad parts either with bone cutters, snap them off if possible, or use a demel (which is my go-to.) Once you have the ones with the RTN (Rapid Tissue Necrosis) chopped off I would consider doing the hydrogen peroxide dip on what's left.
You'll need to act fast on this becuase they can be wiped out in a day or two without attention.
Part 2 of this is that water chemistry may be at fault here, or in another case perhaps there was just an injury that caused the RTN and it spread to others (I have had this happen before). It would be important to have an accurate account of Nitrates and Phosphates along with what you dose, if anyhting, for trace elements.
